1. Field of the Invention
The present invention relates to a circularity measuring apparatus and a measurement value correcting method for circularity measuring method.
2. Description of the Related Art
Conventionally, a circularity measuring apparatus (a circularity measuring machine) that measures a circularity of a circular object such as a cylindrical object has been known. For example, in this circularity measuring apparatus, an object to be measured (a work) having a circular section such as a cylindrical object is placed on a rotatable mounting base, a tip terminal (a probe) is brought into contact with the surface of the work, and a displacement of the tip terminal associated with the rotation of the work is measured, thereby measuring an outer shape of the circular section.
For example, Japanese Unexamined Patent Application Publication No. 1-259211 describes a diameter measuring apparatus of a circularity measuring machine. The circularity measuring machine includes a horizontal arm guiding a contact of a first detector horizontally and in a diameter direction with respect to a cylindrical work, a support frame for the first detector provided at a tip of this arm and allowing the contact of the first detector to make contact with two points at diameter positions, and a second detector for diameter measurement to detect a horizontal movement amount of the horizontal arm. In this apparatus, in advance, a master piece is first set on a rotary base, and the contact of the first detector is brought into contact with a right side surface of the master piece and a measurement value is obtained from the second detector. Next, the contact is brought into contact with a left side surface of the master piece and another measurement value is obtained from the second detector. Then, using these two measurement values from the second detector, an error value of this apparatus is calculated based on known dimensions of the master piece. Then, a work is set in place of the master piece, and a diameter dimension is similarly measured for error correction.
Also, Japanese Patent No. 4163545 describes a reference jig for a circularity measuring machine, the reference jig obtaining information about an origin of the circularity measuring machine and performing calibration of a detector for measuring a surface shape of a measurement target. This reference jig is removably placed on an upper surface of an XY table on a rotary table. The reference jig is provided with a mounting base formed in a stepped disk shape and a calibration master that is provided an upper step part of the mounting base to allow sensitivity calibration of a probe (a detector). Above the calibration master, the reference jig includes an origin ball (a reference ball) which is arranged so as to enable to measure an X-axis direction of a lowermost surface and an uppermost surface and a Z-axis direction of a right side surface and a left side surface of the calibration master. Positional deviations of a stylus (a sensor) provided to the probe are obtained for respective postures of the probe and as correction values. In this art, the reference jig for a circularity measuring machine is placed on a measurement-target rotary mechanism, and the sensor of the detector of the circularity measuring machine is brought into contact with the reference ball, thereby obtaining origin information of the circularity measuring machine. Also, the sensor of the detector is related to a calibration master, thereby performing sensitivity calibration of the detector.